I think the list of mid season promotions may not be that high. Very few are forcing it yet - T. Hall is one who should be moved, and Boeve just was promoted. On the pitching side - I also think that a lot (Misio, Woessner, Blalock, Wichrowski) will stay where they are as they build up innings, and Wichrowski is in his first full season. Like Logan Henderson last year, even if they are doing well they may stay put to keep building up innings and refine the approach.
I think the older (for their level) relief pitchers (Yoho, Hunt) for sure. Hitters I see T Hall, and possibly E. Fernandez and M Wood as candidate given age and production so far. And Guilarte could move up with his cohorts (Areinamo and Barrios).